net: sh_eth: add support for SH7757's ETHER

The SH7757 has 2 Fast Ethernet controller (ETHER) and 2 Gigabit Ethernet
Controller (GETHER). This patch supports 2 ETHER only.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>